1. Field of the Invention.
This invention relates to attachments for driveshaft housings for boat engines generally and, in particular, for driveshaft housings connecting boat engines such as outboard, inboard-outboard and the like to the propeller. The attachment is designed to protect humans, manatees and other creatures in the water from the propeller, fins, and other parts of the housing, while also protecting the propeller, the fins and the like, and improving the efficiency of operation.
2. Description of the Prior Art.
The prior art has many examples of devices for protecting the propeller and submerged boat propulsion parts. However, these devices do not protect creatures in the water very well. Further, the prior art devices reduce the efficiency of the propulsion units by adding undesirable drag loads. Some of the prior art attachments are removable, which could reduce the drag load after reaching open water, but are really removable only when the boat is essentially in a dock or dry docked situation. Those that could be removed when the boat is under way or in open waters may lose attaching parts and/or are not as stable as desired to reduce vibration problems.
U.S. Pat. Nos. 1,009,635; 1,869,977; Re. 18,602; 2,054,374; 2,140,099; 2,355,842; 2,963,000; 2,985,133, 3,965,845 and 4,096,819 are examples of propeller guards that are essentially permanently attached in that they cannot be readily removed when the boat is under way or in open water. Removability is very desirable, because such guards are added drag loads.
Further, none of the devices protect creatures in the water very well. That is, fins or tines are spaced so far apart that arms, hands, fingers, fins, etc. can go between them and be damaged by the propeller. In some, the circle scribed by the propeller radius extends outside of the protection zone of the guard. In others, a keel-like support portion can do substantial impact damage to a swimming creature. Moreover, in some designs, the skag or gear housing or other parts are forward of the protective zone and can do substantial impact damage. Finally, there are many sharp edges that are harmful, whether designed for cutting weeds or just sharp by the nature of their design.
U.S. Pat. No. 2,470,874 discloses a propeller guard that can be pivoted up out of the water. However, the fork arms provide no protection for swimmers and, in fact, are hazardous themselves because the fork arms have knife-like forward edges.
U.S. Pat. No. 2,972,977 discloses a propeller guard which affords more protection than some of the devices because an object engaging shoe is held behind and below the propeller by a pair of spaced, vertical support arms that are pivotally mounted on the transom. A push block carried about half-way down on the support arms pushes against the forward part of upper housing 16 to pivot the propeller and housing out of the water when the shoe strikes an object under the water.
However, the solid shoe adds a very substantial drag load that reduces the efficiency of the propulsion unit. While the device might be removed if the boat were dead in the water, it is very difficult because, after removal of the mounting from the transom, the unit must be lowered much further into the water so that the push block can be passed below the skeg. If the motor is running and the propeller is turning, removal is very dangerous because either one of the support arms or the push block may strike and damage the propeller. Thus, the outboard motor attachment is essentially permanently mounted because the boat must be either in dry-dock, or docked with the engine not running, for safe removal.
The shoe might have been designed to assist the boat in planing, either at full speed or at lower speeds in regulated waters. However, not only is there no teaching or suggestion that such was intended, but the upper part 52 of the shoe 50 has a reduced width to space the support arms apart. In addition, upper part 52 is angled toward the rear, so that when the boat is under way water passing over part 52 actually pushes the part 52, downwardly to interfere with any planning effort.
U.S. Pat. No. 2,319,640 discloses a propeller guard which provides a better protection zone than most. However, the blade-like fingers can cut and injure creatures in the water. Further, while the inventor states that his device reduces turbulence, there is still a substantial amount of drag load and turbulence and therefore less efficiency at slower speeds. Therefore it would be very desirable to be able to remove the device when under way and in open water at higher speeds.
However, the guard is attached under the water line to the cavitation plate by a wing nut to a plate bolt. The device is subject to nut loosening and loss of the device as a result of the vibration of the blade-like fingers. To detach the guard, one has to work under water with the possibility of loss of the wing nut and/or guard. Moreover, the nut/bolt combination may corrode, resisting or preventing removal without tools. Thus, this propeller guard is again essentially a permanently mounted device which hampers efficiency at all speeds.
U.S. Pat. No. 4,565,533 discloses a propeller guard which does not provide adequate protection for swimmers, manatees, etc. because the rearwardly extending ribs are much too far apart. However, it does disclose a quick-release system to enable removal under way or in open water to improve propulsion efficiency at higher speeds when swimmers, manatees are not in, or not supposed to be in, the water. While a safety loop 46 on the main body is provided for attachment to a safety line to prevent loss by dropping the guard, the other essential part 44 of the attaching system does not have any means for preventing loss of the part. This is a major flaw since the boat may have to return through swimmer and manatee waters without protection for them.
This device has a further problem in that the ribs are going to vibrate, affecting the stability of the device and increasing turbulence. While a sleeve 38 is provided to receive the skeg, there is a substantial length of the main rib 25 between the skeg and the quick-release that isn't anchored in any way.
U.S. Pat. No. 4,680,017 discloses a propeller guard that isn't satisfactory because of the large drag load, the damage that the sharp edges of ribs 58 can do to swimming creatures, and the inability to easily remove or reinstall the guard in open water or while under way--with the added possibility that the guard may be dropped in the water and lost. However, the device does show a frame member 52 which is channel shaped to extend around leading edge 18 of lower housing 16. This provides structural support for the ribs 58 and protects leading edge 18 and skeg 22 from damage. On the other hand, because water is flowing directly past frame 58 between ribs 58, there is no deflection of a swimmer or a manatee by a diverted water flow, and impact against the frame 58/edge 18 is direct and damaging.
The function of a propeller is to produce thrust along the axis of the propeller shaft to drive the boat or ship, by giving momentum to the water it displaces in an astern direction. In pushing the water backwards, a reaction force is developed to push the craft forward. It is therefore desirable to maintain the axis of the propeller substantially parallel to the horizontal axis of the craft when the hull is in its most efficient operating position in the water. Most craft that will be using this invention will have planing type hulls, as opposed to displacement hulls. The planning type hull operates most efficiently when the stern of the boat is raised by the speed of the boat in open waters. However, this invention will be primarily used in speed restricted waters, and then removed in open water.
As noted above, the prior art devices of this general type add drag load when used. Further, most of them cause substantial turbulence which further reduces the efficiency of the propeller. None of the them react with the water passage to lift the stern of the boat to a more efficient operating position.
Accordingly, it is an object of this invention to provide an attachment which allows the water flow to the propeller to be as free of turbulence as possible, while also reacting with the passage of water to urge the stern of a boat upwardly toward a more efficient operating position.
It is a another object of this invention to provide an improved housing attachment for protecting swimmers of all types from injury by propulsion units of boats, while still providing protection for the propulsion units themselves.
It is a further object of this invention to provide such an improved attachment which is designed to improve the efficiency of the propulsion unit by reducing the effect of the added drag load of such guards.
A still further object of this invention is to provide such an improved attachment that can be readily removed when the boat is out of waters with switching creatures that might be injured, without fear of losing the attachment or damaging the propeller, so that the boat may then be operated at all speeds at top efficiency. It is a further object to be able to readily re-install the attachment before entering waters with swimmers, manatees, etc.
It is also an object to provide means to insure stability to the attachment structure to prevent undesirable vibration, even though the attachment may be readily removed and re-installed.